Control means for hydraulic pump and motor systems



April 21, 1953 w. H. MARSH ETAL 2,635,428

CONTROL MEANS FOR HYDRAULIC PUMP AND MOTOR SYSTEMS Original Filed Aug.14, 1946 2 SHEETS-SHEET 1 M o F /v Q F 1 1S 3 a v Fig. 2

INVENTORS Wa/fer H. Mani William I. Smith A Horneys April 21, 1953 w. H.MARSH EIAL CONTROL MEANS FOR HYDRAULIC PUMP AND MOTOR SYSTEMS 2SHEETSSHEET 2 Original Filed Aug. 14, 1946 4 Q I 0 R v n 5 I I 5 II x H5 01 0 m W Q a! 5 E 94 7 3 B .0 Ir v 1v. 2 /v 4 JA 5 3 9 3 Z :21 2 a? fMy m/ 14% w s m m \K\ M SK J W M. 4 h lHL r F P a pk HM H 4 W a M 0 l aw a a A IIH 2 II F m 4. 2' 5 B l 7 M 3 K Vu r QIIIII d d b c (a PatentedApr. 21, 1953 CONTROL MEANS FOR HYDRAULIC PUMP AND MOTOR SYSTEMS WalterH. Marsh, Grafton, and William I. Smith,

Wilkinsburg, Pa., assignors to Rockwell Manufacturing Company,Pittsburgh, Pa., a corporation of Pennsylvania Substituted for abandonedapplication Serial No.

690,574, August 14, 1946. This application August 9, 1948, Serial No.43,324

1'7 Claims.

This invention relates to control means for hydraulic apparatus and moreparticularly to simple and efficiently operating means for controllingthe transmission of hydraulic fluid from a constant displacement pump toa motor to drive the latter at a predetermined speed with a minimum lossof energy. The present application is substituted for application S. N.690,574, filed August 14, 1946, now abandoned, which in turn is acontinuation-in-part of an abandoned application S. N. 504,130, filedSeptember 28, 1943.

It is one of the principal objects of the invention to provide a novelvalve mechanism connected between a constant displacement pump and fluidmotor, whereby all or any part of the fluid discharged from the pump mayby-pass the motor so that only that portion of the fluid pressure willbe utilized, which is required to drive the motor at a predeterminedspeed.

It is another object of our invention to provide a valve mechanismhaving a symmetrical porting arrangement whereby the direction ofoperation of the motor may be reversed at will.

A further object of the invention is to provide control means for thehydraulic motor which will be effective to hydraulically lock the motorwhen the latter is not in operation.

It is an additional object of the invention to provide a novelcombination and arrangement of auxiliary by-pass valves within a mainvalve and controlling the eifective fluid pressure supplied to themotor.

Another object of the invention resides in the provision of a controlvalve assembly and connections between said assembly and the pump andmotor, whereby the main control valve and the auxiliary by-pass valvesare operated by fluid pressure.

A further object of the invention resides in the provision of a pilotvalve of novel construction having means providing for the introductionof gradual intake, exhaust and stabilizing clearances to effect smootheroperation of the control valve elements.

It is also one of the objects of the invention to provide means in thecontrol system driven by the motor to produce a slight pulsatory actionof the fluid in the valve mechanism which will materially augment thesensitive response of the movable valve elements to the fluid pressures.

With the above and other objects in view, the invention comprises theimproved control means for hydraulic apparatus and the construction andrelative arrangement of its several parts as will hereinafter be morefully described, illustrated in the accompanying drawings andsubsequently incorporated in the subjoined claims.

In the drawings, wherein we have illustrated one practical embodiment ofthe invention, similar reference characters designate correspondingparts throughout the several views.

Figure 1 is a diagrammatic plan view illustrating one arrangement of theprincipal control units in the fluid transmission connections betweenthe pump and motor.

Figure 2 is a similar diagrammatic view taken at section 2-2 of Figure 1in elevation showing the connections between the pilot valve and themain control valve.

Figure 3 is a semi-diagrammatic sectional view on the line 33 of Figure1 illustrating the connections between the main control valve and thepump and motor.

Figure 4 is a vertical sectional view on an enlarged scale illustratingthe main valve assembly with the valve elements in neutral or normalposition and showing the dither valve connected with said main valveassembly and with the pressure regulating unit.

Figure 5 is a horizontal sectional view taken substantially on the lines5-5 of Figure 4.

Figure 6 is a detail view partly in section, showing the dither valveconnected to the pump shaft.

Figure 7 is a sectional view illustrating a conventional type of pilotvalve.

Figure 8 is a similar view showing our improved pilot valveconstruction.

Referring in further detail to the drawings, in Figures 1 and 2 thereof,we have illustrated the principal units of our control means connectedin the fluid transmission system between the pump N and hydraulic motorM. These units comprise a main valve assembly V having an inletconnection A with the discharge side of the pump and supply anddischarge connections B with the ports of motor M; the pilot valve Pconnected by conduits C with fluid pressure chambers at opposite ends ofthe main valve; a dither valve unit D also connected by conduits E withsaid pressure chambers of the main valve; and a regulator valve unit Rinterposed in the bleed line connection F between the pump dischargeconduit A and the dither valve D.

For purposes of illustration, we have shown the pump and motor asidentical hydraulic mechanisms which may be used interchangeably as apump or motor. Therefore, the same reference numerals have been appliedto corresponding parts of these two mechanisms. As shown in.

Figure 3, the pump and motor are of the constant displacement type andcomprise a housing supporting a division plate 2 between spaced fluidinlet and outlet ports thereof, A cylindrical rotor 3 is keyed to ashaft 4 suitably journalled in the end walls of housing Semi-cylindricalvanes 5 are journalled in the rotor and are 1'0,- tated by a gear systemso arranged that the flat surfaces of the vanes remain always paralleland thus have the proper clearance over the division plate 2, Because ofthe symmetry of these mechanisms, operation in either direction isinherently optional. In the system illustrated the pump rotatescounter-clockwise so that port 5 is the intake and port 1 the discharge.The direction of operation of the motor depends upon which of the ports8 or 9 receives the fluid from the pump. Fluid may be supplied to theintake port of the pump from a sump or reservoir. Further detaildescrition of the pump and motor are not required for the purposes ofthis present explanation, for which reference may be had to Patent No.2,274,206 issued February 24, 1942, to Walter H. Marsh.

The pump N is driven from an external power source and, assuming thatthe rotor 3 is rotated in anti-clockwise direction, the port 6 is theintake port while port 1 is the discharge port with which transmissionconduit A is connected.

The main valve assembl V includes the cored manifold M suitably attachedto both the pump and motor and so cored as to provide a fluid channelconnecting the manifold bore |2 with pump outlet conduit A and the twomotor ports 8 and 9. The opposite ends of bore i2 are threaded toreceive suitable closure or cover members l3. The pump intake port 6 mayopen directly into the sump through an opening provided in valvemanifold M.

Mounted in the manifold bore I2 is a machined valve sleeve l4. The mainvalve i5 is axially slidable in this sleeve and is normally urged to acentral or neutral position by means of coil springs I6 compressedbetween the closure members l3 and suitable shoulders I! formed on theends of valve member i5.

The manifold M and the valve sleeve l4 are provided with a series ofaxially spaced registering ports which includes control ports [8 atopposite ends of the valve unit, a central port 2| directly connectedwith pump outlet conduit A and intermediate motor connecting ports 29and exhaust ports I!) respectively. Ports |9 open through the manifolddirectly into the sump or fluid supply reservoir. Preferably a bafileplate 22 is mounted directly below the lower exhaust port |9 to preventthe fluid from taking the shortest path through the sump back into thepump intake port 6. This baflie has a marked effect on lowering thetemperature of the fluid, when space limitations require the use of aminimum volume of fluid.

The main valve member I5 is of generally cylindrical shape and providedwith a central land 23 and two end lands 24. The reduced cylindricalterminal bosses 25 of the valve member are received within the springsl6 and also serve to limit axial movement of the valve member by contactwith the covers |3. The spaces between the end lands 24 of the valvemember and covers |3 constitute fluid pressure chambers '26 whichrespectively open into the upper and lower control ports l8. From theouter surface of each land 24 the periphery of valve member |5 graduallytapers inwardly to a small 4 diameter section adjoining the center land23, for a purpose which will become apparent from the followingdescription.

The main valve |5 has an axial bore 21 intersected by a plurality ofspaced radial holes 28 drilled through the center land 23. Also smalldiameter radial holes or apertures 29 are drilled radially through eachof the end lands 24 at its inner end portion and in diametricallyopposite sides thereof. The openings 28 and 29 provide flow ports forthe fluid to and from the axial bore 2'! and are so located as to permitpartial or total blocking of the fluid flow through bore 2'! by theunbroken surfaces of the main valve sleeve l4 upon movement of the valvemember l5. In the preferred construction of this valve member, thecenter land 23 is of slightly less diameter than the end lands 24 toavoid any possibility of binding between the edges of the central landand the edges of the central slots or ports in the sleeve [4. The endchambers 26 are each connected through the upper and lower control portsI8 and couplings [8 to the dither valve D and also through theconnecting conduits C to the pilot valve P. The two motor ports 20 areconnected by transmission conduits B with the motor ports, while asabove noted, the central port 2| is in fluid communication with the pumpdischarge port I.

An auxiliary by-pass valve is positioned in each end of the axial boreof the main valve member i5. Each of these auxiliary by-pass valvesincludes the member 3| which is axially urged in one direction to normalposition by spring 32 interposed between one end of said valve memberand a tubular plug 33 secured in the end of the valve member |5 by a pin34 extending transversel through the boss 25.

The axial travel of valve member 3| under the pressure of spring 32 islimited by a transverse pin 35 fixed in valve member I5 and extendingacross the axial bore '21 thereof through diametrically opposed slots 31and the axial bore 36 of valve member 3|. The tubular stops 33 permitequalization of fluid pressure between the chambers 26 and the outerends of valves 3| and prevent hydraulic locking of said valves in fixedposition with respect to the main valve l5. The two legs 38 formed byslots 3! coacting with pin 35 restrain the valve member 3| againstrotative movement relative to valve member l5. The bore 36 in spacedrelation from the outer end of the valve member is intersected bydiametrically opposite openings 39 in said member which are in axialalinement with the respective groups of openings 29 in the valve member5 for movement into and out of registration therewith. By thisconstruction, the passage of fluid through the openings 29 in the main,valve may be controlled not only by movements of the main valve withrespect to sleeve l4 but also by the relative movement of the auxiliaryvalves 3|. It will thus be apparent that any fluid entering the bore ofthe main valve l5 through the openings 28 must flow axially along thebores of the two valve members and through the openings 39 in the valvemembers 3| before it can be exhausted through the openings 29 in themain valve and the exhaust ports IS.

The pilot valve assembly P is shown in a preferred embodiment thereof inFigure 8 of the drawing. This valve, which controls the operations ofthe main valve assembly, includes the housing 40 having a cylindricalbore 4| into which a sleeve 42 is pressed, an upper port 43 mountedwithin the bore of the sleeve 42. Thisvalve member is providedsubstantially for its full length with the thread 41, the intermediateconvolutions of which are in contact with the wall of bore 45. Theopposite end portions of the thread 41 gradually decrease in diameter asindicated at 48 in successively increasing radially spaced relation fromthe wall of bore 45 to the terminal convolutions. A pin 45 isdiametrically disposed across the lower end of bore 45 in sleeve 42 tolimit the downward axial movement of valve member 46 therein. Suitablemeans 50 is provided at the upper end of the valve member by which itmay be readily shifted in the bore 45 either manually or by a suitablemechanical connection therewith.

In order that the operational advantages of the pilot valve 45 may beclearly understood and for purposes of comparison, we have shown aconventional type of pilot valve in Figure 7 of the drawing. This valvecomprises a cylindrical rod a having two lands b and c axially spacedapart to coincide with the inlet ports d and e respectively. The widthof these lands is slightly less than that of the ports d and e.Therefore, when the valve is in a central or neutral position, there areslight clearances as indicated at f and g between the lands and theupper and lower sides of the respective ports. These clearances may bereferred to as exhaust and stabilizing clearances respectively. It willbe seen that any fluid entering one of the ports 11 or 6 when the pilotvalve is centrally positioned, will have several possible paths ofescape. Thus, the fluid may flow through the upper exhaust i into thesurrounding sump, or through the upper stabilizing clearance g into thespace between the lands 1) and c and hence, through the oppositestabilizing clearance 9 into the conduit connection which leads to theother end chamber 28 of the main valve, or mainly around the land andinto the surrounding sump.

Normally, the clearances ,f-f provide relief for the pressures in valvechambers 26. If however, the valve member a is given an axial movementso that the exhaust clearance of one land is closed simultaneously withthe closing of the stabilizing clearance g of the other land, then thefull pressure developed by the regulator unit R will bear on that end ofthe main valve member 15 corresponding to the port of the pilot valvewhose exhaust clearance is closed. For smooth and efiicient action, suchan hydraulic locking at one end of the main valve may be prevented. Thistype of pilot valve has the additional undesirable feature that in theaxial movement of the valve member one of the stabilizing clearances maybe entirely closed, which can result in an unstable operation of themain valve member.

Our new pilot valve construction will avoid the difficulties abovementioned, since in the operation thereof, none of the clearances isever entirely reduced to zero. When the pilot valve member 46 and mainvalve member l are in the central or neutral position, the fluidpressure in the end chambers 26 of the main valve will become equalizedas the fluid may readily flow through the conduit connections C andports 43 and 44 between the convolutions of the thread '41 6. and intothe sump or reservoir and the rate of flow may be varied by movement ofthe pilot valve member 46 so as to change the number of convolutionsbetween ports 43 and 44 and the sump or reservoir. The variation in flowdue to iovement of pilot valve member 46 may be increased by taperingthe end threads 41 so that when one of the tapered portions is oppositeto the associated inlet port, there will be a larger flow of fluid fromthe corresponding end chamber 26 of the main valve into the sump orreservoir While the fim'd pressure regulator R will build up pressure inthe other end chamber 26, notwithstanding the continued relatively smallflow of fluid from the latter chamber through the other inlet portbetween the full diameter convolutions of the thread 41 opposed to thelatter part. The clearances f and g above referred to in connection withconventional type of pilot valve are represented in the valve of Figure8 not only by the space between the thread convolutions but also uponsufficient movement of the valve by the space developed between thetapering portions ofthe valve and the bore of the valve sleeve, it beingnoted that the increase or decrease of such clearances occurs graduallyin the shifting of the valve, resulting in a smooth operation of themain valve mechanism.

The dither valve assembly is shown in Figures 4 and 6. This valve ismounted in the axial bore 52 of a housing 5|. This bore is interested bythree radial openings 53, 54 and 55 respectively spaced apart Theopenings 53 and 54 are outlet ports connected by the couplings I8 to therespective end chambers 26 of the main valve assembly, while opening 55is an intake port connected with the outlet of pressure regulator R bythe conduit 56 which is preferably provided with a suitable type ofneedle valve 5'! by means of which the volume of fluid flow to thedither valve may be regulated.

The dither valve 58 is preferably driven from the shaft 4 of the pumpand comprises a short steel cylinder having three flat, symmetricallyarranged peripheral surfaces 59 formed thereon. Into one end of thisvalve member 58 two pins 60 are fixed in longitudinally projectingrelation therefrom to fit into registering longitudinal bores 6|provided in one end of the pump drive shaft 4. Thus, the valve member 58will revolve in the bore 52 at the same speed as the pump rotor. By theprovision of the flattened surfaces 59 on the valve member, the rotationthereof results in a rapid succession of fluid impulses or pulsationswhich are transmitted through the ports 53 and 54 and couplings IE tothe end chambers 26 of the main valve assembly V. Thus, staticpositioning of the valve elements is avoided with a more sensitive andrapid response of said elements to relative movement under the controlof the pilot valve P. The effective value of the pulsations from themovement of the valve 58 may be altered by adjustment of valve 5! tochange the rate of flow to the dither valve, as well as by themodification of the constructural design of the valve member.

In the operation of the above described mechanisms, assuming first thatthe main valve l5 and pilot valve 46 are in neutral position as shown inthe drawing, the entire output of the pump N, with the exception of thesmall portion entering the intake of the regulator unit R which isdelivered under predetermined pressure through the dither valve unit Dto the end' chambers 26 of the.

main valveassemblyv, enters the intake port' 2| of the main valveassembly. Fluid flow into the sleeve I4 is substantially entirelyblocked by the central land 23 of the valve member 15. Thus, the fluidmust pass through the radial openings 28 into the axial bore 21 of valvemein ber l and then axially in each direction through said bore and thebores 36 of auxiliary valve member 3| where, in this neutral position,the fluid will flow through the holes 39 in the latter valve member andholes 29 in the main valve l5 and into the sump or fluid reservoirthrough the exhaust ports IS in the main valve manifold.

The fluid pressures supplied through regulator R and dither valveassembly D to the end chambers 26 of the main valve assembly areequalized, since there is a continual equal leakage of fluid from theseend chambers through the pilot valve P to the sump or reservoir. Thus,the main valve l5 will remain in its hydraulically balancedneutralposition.

Since all of the fluid except the small portion in the controlpassage-ways is by-passed through the main valve assembly, the motorunit M is not operated and no effective work is done. In fact, the motoris substantially hydraulically locked in a stationary position since asmall volume of fluid will pass the. center land 23 of the main valveinto the upper and lower motor ports 23.

Referring new to Figure 3 of the drawing, assuming that it is desired todrive the motor in anti-clockwise direction, the pilot valve 46 is movedvertically upward to position the lower tapering convolutions. of thethread 41 with respect to port 44, thus exhausting fluid from the lowerchamber 26 of the main valve assembly in greater volume to rapidlyreduce the pressure thereof. The relatively higher fluid pressure in theupper chamber 26 is then effective to move the main valve member l5:downwardly, uncovering the port 2| in the valve sleeve so that the fluidmay flow upwardly into upper port 20 and into the port 9 of the motor.The lower port 20 of the valve assembly'is simultaneously connected withthe lower exhaust port l3 so that the fluid will be exhausted throughthe motor port 8 and port 19 of the valve assembly to the sump orreservoir. This downward movement of main valve l5 also results in adecrease in the by-pass flow of fluid through openings 29 into theexhaust port, thereby increasing the fluid pressure within the bore ofvalve member I5 which can force the auxiliary by-pass valve members 3|outwardly with respect to the main valve member, moving the openings 39thereof wholly or partially out of registration with the openings 29 invalve member l5 and thus further decreasing the by-pass flow of fluid toexhaust port [9 which results in a secondary increase of the fluidpressure supplied to the motor port 9 to compensate for a suddenincrease in resisting torque of the motor. Thus, by proper adjustment ofthe pilot valve member 46 and auxiliary by-pass springs 32 to controlthe release of pressure from the lower valve chamber 26 and the axialmovement of valve members 15 and 3|, the motor may be driven at anyselected speed from zero to maximum over a broad range of motorresisting torques.

Obviously, owing to the symmetrical porting arrangement of the mainvalve assembly, the

motor may also be driven in the reverse or clockneutral position torelease the fluid pressure from.

the upper chamber 26' of the main valve assembly so that the main andauxiliary valve will function as above described to connect the port 2!with the lower motor port 20 while the fluid is exhausted through motorport 9 and returned through the upper exhaust port l9 to the sump orreservoir.

From the foregoing description, it will be seen that we have providedsimple and reliably functioning means for establishing variable fluidpressures and rates of flow in the main valve mechanism which controland determine the movement of the valve members relative to each otherand to the ports or passages in the valve manifold. Thus, through asingle control valve unit, the motor or other apparatus may be driven atany selected speed between zero and maximum, and in either direction;while, when the motor is idle and the pump is in continuous operation,substantially the entire output of the pump is by-passed around themotor through the valve mechanism with little pressure drop, and hencesmall loss of energy. Also, as above noted, by maintaining pulsatory orfluctuating fluid pressures in the end chambers of the valve manifold, astatic condition of the movable valve parts is avoided so that they willbe sensitively responsive to any adjustment of the primary or pilotcontrol valve 46. It will of course, be understood that the abovedescription of the pump and motor is merely suggestive, and that ourimproved valve control mechanism may be employed in connection withsimilar units of well known mechanical construction.

The invention may be embodied in other speciflc forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In combination with hydraulically operated apparatus and a source offluid pressure, a fluid distributing system comprising fluidtransmission channels to and from said apparatus and pressure source,and valve mechanism interconnected with said transmission channels, saidmechanism comprising a manifold having a central inlet port and fluidsupply and exhaust ports connected with the apparatus at each side ofsaid inlet port together with a chamber at each end of the manifoldconnected with the fluid pressure source, a main valve in said manifold,a by-pass valve subject to inlet fluid pressure mounted in each end ofsaid main valve, said main and by-pass valves having coacting means toby-pass fluid to the pressure source, and a control valve connected withsaid end chambers to hydraulically balance the main valve in neutralposition and interrupt fluid flow through said mechanism to theapparatus, said control valve being operable to selectively exhaustpressure fluid from said end chambers and reverse the direction ofoperation of the apparatus at will.

2. The combination defined in claim 1, together with spring meansbiasing said by-pass valves to normal position to by-Dass substantiallythe entire volume of fluid from the inlet port to the fluid pressuresource.

3. In combination with hydraulically operated apparatus and avolumetrically constant source of fluid pressure; a fluid distributingsystem comprising fluid transmission channels to and from said apparatusand pressure source, and valve mechanism including a main valveoperative in response to differential fluid pressures to distributefluid from said constant volume source in variable volume to saidapparatus and from the apparatus to the pressure source, relativelymovable auxiliary valves mounted at opposite ends of the main valve,said main valve having a passageway in fluid communication with thepressure source and means controlling the volumetric flow of fluid fromthe pressure source to the apparatus and return flow to the pressuresource, said main valve having a by-pass at each end, said auxiliaryvalves being operable by fluid pressure in the said passageway and eachhaving means cooperating with the respective by-passes of the main valveto control the volume of by-passed fluid and modify the fluid pressuresupplied to the apparatus.

4. The combination defined in claim 3, wherein the auxiliary valves andthe flow transmitting connections between the main valve and theapparatus are arranged with respect to the connection between said valveand the fluid pressure source for the controlled operation of saidapparatus in reverse directions.

5. The combination defined in claim 3, together with a pilot valve influid communication with the main valve and the fluid pressure sourceand operable to create difierential fluid pressures in said main valveto actuate the main and auxiliary valves as a unit in each direction.

6. The combination defined in claim 3, together with difierentialpressure producing means connecting the fluid supply source with themain valve to selectively move said valve and the auxiliary valves as aunit in each direction, and a power driven dither valve connected withthe main valve and operative to pulsate the fluid medium and preventstatic positioning of the relatively movable valve parts.

'7. The combination defined in claim 3, together with a pressureregulating valve and means connecting said valve with the main valve andwith the constant fluid pressure source, and a power driven dither valveinterposed in the connecting means between the main and regulatingvalves to produce a pulsatory movement of the fluid medium and the mainand auxiliary valves.

8. In combination with a hydraulic motor and a constant fluid pressuresupply pump, fluid flow control means between the pump and motorcomprising a valve assembly including main and auxiliary reciprocatingvalve members operative respectively to produce a primary modificationof fluid pressure supplied to the motor by said pump and a secondarymodification of fluid pressure to compensate for varying loads on themotor, said auxiliary valves being subjected on one side to the fluidpressure from said pump, means forming pressure chambers at each end ofsaid main valve and the other side of said auxiliary valves, saidpressure chambers being hydraulically connected to said pump, and pilotvalve means connected with said pressure chambers and operable tocontrol the pressure in said chambers and thereby the effectiveoperation of said main and auxiliary valves.

9. The combination defined in claim 8, together with means operativelyconnected with a driven part of the pump operable to control the supplyof fluid to said pressure chambers to produce pulsatory fluid pressuressaid pressure cham- 1Q bers acting upon said main and auxiliary valvemembers.

10. The combination defined in claim 8, together with a pressureregulating valve in fluid communication with said chambers and with thedischarge side of the pump, said pilot valve in fluid communication withsaid chambers comprising spaced means constructed to control the exhaustof fluid pressure from the respective chambers and to maintainstabilizing pressures therein when the exhaust is fully closed.

11. In combination with a hydraulic motor and a constant fluid pressuresupply pump, fluid flow control means between the pump and motor,comprising a valve manifold having an inlet port connected with thedischarge side of the pump, a port at each side of said inlet portconnected respectively to inlet and discharge ports of the motor,exhaust ports to discharge fluid from the respective last named manifoldports to the intake side of the pump, and a fluid pressure chamber ateach end of the manifold; a main reciprocating valve in said manifoldhaving a bore and a port variably controlling the distribution of fluidbetween said manifold inlet port, the motor ports thereof and said valvebore, said bore being in fluid communication with said end chambers,auxiliary valve members reciprocating in opposite ends of said bore andactuated by fluid pressure therein, means connected with said chambersoperative to create differential fluid pressures in saidend chambers andmove the main and auxiliary valves as a unit in one direction, said mainand auxiliary valves having co-acting by-pass means connecting said borewith the exhaust ports to variably modify the fluid pressure supplied tothe motor under the control of said main valve.

12. The combination defined in claim 11, in which said means connectedwith the end chambers of the valve manifold comprises a pilot valvehaving means to selectively control the exhaust of pressure fluid fromsaid chambers and to maintain a stabilizing pressure therein in allpositions of said pilot valve.

13. The combination defined in claim 11, in which baffle means isinterposed between the manifold exhaust ports and the intake side of thepump, together with additional means connecting each of said endchambers with the discharge side of the pump including a power drivendither valve operative to produce a pulsatory movement of the fluidmedium and the main and auxiliary valves.

14. In combination with hydraulically operated apparatus, avolumetrically constant source of fluid pressure and fluid distributingmeans connected between said apparatus and pressure source, including avalve mechanism, fluid pressure means for operating said valvemechanism, a pressure regulating valve connecting the pressure sourceand said fluid pressur'e means, and primary control means including avalve casing having spaced exhaust ports in fluid communication withsaid fluid pressure means and a pilot valve operable within said casinghaving adjustable means constructed to cooperate with said exhaust portsof said casing to control the exhaust of fluid pressure from said fluidpressure means while maintaining stabilizing pressures therein in allpositions of said pilot valve.

15. In combination with hydraulically operated apparatus, avolumetrically constant source of fluid pressure, fluid distributingmeans connected between said apparatus and pressure source, including avalve mechanism, fluid pressure means for controlling said valvemechanism, a pressure regulating valve connecting the pressure sourceand said fluid pressure means, and primary control means for said fluidpressure means including a valve casing having spaced exhaust ports influid communication with said fluid pressure means, a pilot valveoperable within said casing having means constructed to cooperate withthe exhaust ports of said casing to control the exhaust of fluid fromsaid fluid pressure means while maintaining stabilizing pressurestherein in all positions of said pilot valve, said pressure sourcecomprising a constant volume pump having an intake in communication witha fluid containing sump in which the pilot valve casing is immersed withits bore in fluid communication with the sump, and wherein said pilotvalve is reciprocable in said casing and said control means thereofcomprises spaced helical threads on said valve having tapering endportions of progressively decreasing diameter to the terminals thereofand cooperating with the respective ports of said casing to exhaustfluid in variable volume from said fluid pressure mechanism and tomaintain stabilizing clearances between the pilot valve and casing inall positions of said valve.

16, In combination, a source of fluid pressure, a reversible fluid motorhaving two ports, valve means connecting said source and said two ports,said valve means including a member movable to connect either of saidports to said source and vary the volume of fluid entering the connectedport, a pressure chamber at each end of said valve means for moving saidmember, each of said pressure chambers having separate inlet and outletconnections, means for introducing fluid under pressure from saidpressure source into the inlet connections of both pressure chambers,and control means independent of said fluid introducing means forregulating the relative proportions of flow of fluid in said outlets.

17. The combination defined in claim 16 in which the control meanscomprises a pilot valve, means for connecting both outlets to said pilotvalve, a member movable in said pilot valve to regulate the relativeproportions of flow of fluid from said outlets and means for positioningsaid member in any intermediate position between its two limitingpositions.

WALTER H. MARSH. WILLIAM I, SMITH.

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